The Attenuation of Guided Wave Propagation on the Pipelines

• Main Authors: Jyin-wen Cheng, 鄭錦文
• Other Authors: Shiuh-kuang Yang
• Format: Others
• Language: en_US
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/79927264259190151298

博士 === 國立中山大學 === 機械與機電工程學系研究所 === 94 === The guided wave technique is commonly used for rapidly long-range pipeline inspection without removing the insulation of pipes. The torsional mode T(0,1) of the guided waves is usually generated to detect the defects in pipelines, since it has the advantage of being non-dispersive across the whole frequency range. However, a large number of pipelines are carrying fluid, wrapped with the coating material, and supported with clamp for the necessary manufacturing process in refinery and petro-chemical industrials. When these works are employed on the pipeline, the propagating guided waves may vary with the contents of material and how well the material compact on the pipe. Some energy of the incident guided wave in the pipe wall may leak into inside of contents or outside of wrapped materials and reduce the wave propagation distance. The effect of the fluid-filled pipe, the wrapped pipe, and the clamp support mounted on the pipe for guided wave propagation is investigated by both simulative and experimental methods. The wave structure of the T(0,1) mode in the pipes is analyzed by using the DISPERSE software for various cases to evaluate its influence to the guided wave propagation on the pipe. The amplitudes of the reflected signals from various features on the pipe are also measured using pipe screening system for calculating the attenuation of guided waves due to the features. The trend for the results is in good agreement between the experiments andpredictions for all cases of researches in this dissertation. It is found that the low viscosity liquid deposited in the pipe, such as water, diesel oil, and lubricant, has no effect on the torsional mode; while the high viscous of the fuel oil deposited in the pipe attenuates the reflection signal heavily for the pipe carrying fluid. In addition, both the full-filled and half-filled contents in the pipe are also studied in this case. The effects of the half-filled are the same as the full-filled results obtained. For the pipe wrapped with the coated material, the adhesive strength of the coated material is strong, such as bitumen and polyethylene; the attenuation of the guided waves is high; and there is almost no effect for mineral wool coating. Furthermore, the traveling distance of the guided waves in the pipe is also evaluated for various cases of the coated materials. The results indicate that the higher attenuation of the guided waves for the coated material, the shorter of the traveling distance in the pipe. For the clamp support mounted on pipe, the attenuation of the guided waves for the clamp support with a rubber gasket in between the pipe and the clamp is heavier than the case of clamp support without the rubber gasket is. Furthermore, the higher torque setting on the clamp (with or without the rubber gasket), the higher amplitude of the reflected signal is measured for the guided wave propagation. The effect of the frequency excitation is additionally demonstrated in this dissertation. It is noted that the higher amplitude of the reflected signal, the lower frequency excitation; moreover, theresonant effect is observed in the case of the clamp support with rubber gasket during the torque setting in the experiments. Good agreement has been obtained between the experiments and theoretical calculations of this effect.